Release of vesicles enriched in complement receptor 1 from human erythrocytes

Area of Science:

• Hematology
• Immunology
• Cell Biology

Background:

• Human red blood cells (RBCs) release vesicles during Ca(2+)-loading, ATP-depletion, or storage.
• These released vesicles are known to be enriched in glycosylphosphatidylinositol-anchored proteins, such as acetylcholinesterase (AchE) and decay-accelerating factor (DAF).
• Consequently, the remaining RBCs become depleted of these specific proteins.

Purpose of the Study:

• To investigate whether vesiculation induced by ATP-depletion in vitro also leads to a loss of complement receptor 1 (CR1) from RBCs.
• To determine if CR1, a transmembrane protein, is preferentially lost or enriched in released vesicles.
• To assess the functional implications of CR1 loss on the binding of C3b-coated immune complexes.

Main Methods:

• Induction of vesiculation in human RBCs via ATP-depletion in vitro.
• Quantification of CR1, AchE, and DAF levels in both remaining RBCs and released vesicles.
• Measurement of CR1 enrichment in vesicles relative to band 3 protein.
• Assessment of the binding capacity of vesicles and ATP-depleted RBCs to C3b-coated immune complexes.

Main Results:

• ATP-depleted RBCs exhibited a significant loss of CR1, ranging from 15.4% to 33.9%.
• The loss of CR1 was comparable to the loss observed for AchE and DAF.
• Released vesicles were found to be enriched in CR1, with a higher number of CR1 per band 3 protein compared to original RBCs.
• The enrichment of CR1 in vesicles was similar to that of AchE and DAF.
• The binding capacity for C3b-coated immune complexes correlated with CR1 levels, indicating no preferential loss of CR1 clusters.
• Vesicles released during complement (C) attack also contained CR1.

Conclusions:

• In vitro aging induced by ATP-depletion causes a loss of both glycosylphosphatidylinositol-anchored proteins and complement receptor 1 (CR1) from human RBCs.
• Vesiculation is a key mechanism contributing to the loss of CR1 during in vitro aging.
• Further research is needed to determine if vesiculation explains CR1 loss in vivo during RBC aging and in conditions like systemic lupus erythematosus (SLE) or AIDS.